The present invention relates to avoiding recall operations on a tiered data storage system, and more particularly, to a system, method, and computer program product for avoiding recall operations when writing new data to files on a tiered data storage system.
Using conventional space management techniques on a tiered data storage system, data is often migrated from one tier of storage to another tier of storage. Generally, data is stored initially on a higher-cost, more available data storage tier, that uses storage media such as direct access storage devices (DASD). At some point, the stored data may be moved to a lower-cost data storage tier that uses lower-cost storage media such as magnetic tape. If the data is moved from the lower-cost data storage tier back to the higher-cost data storage tier, the operation to move the data is referred to as a “recall.”
When an application, system, routine, etc., has data to update a file with, and that file is stored on the lower-cost data storage tier, that file (data set) must be moved from the lower-cost data storage tier to the higher-cost data storage tier (recalled), so that an update can take place. Once the data set to be updated is on the higher-cost data storage tier, the new data may be written into the data set. With some access methods and/or types of updates, the new data may be placed at the end of the data set. In this case, the data set is recalled and information in the data set does not necessarily need to be read; instead, the new data is simply appended to the end of the data set. Then, the updated data set can be moved back to the lower-cost data storage tier if it meets space management criteria after the update. This wasted I/O causes unnecessary system overhead and causes delays in other job execution. It also causes additional overhead when the updated data set is moved back to the lower-cost data storage tier after updating is complete.